Mass analysis data processing apparatus

ABSTRACT

A product ion spectrum is created on the basis of MS 2  analysis data respectively obtained for a parent compound and a metabolite (S 1  and S 2 ). Additionally, a neutral loss spectrum, in which the mass of each product ion is replaced with a mass difference between the mass of the product ion and that of a precursor ion, is created (S 3 ). Then, a common peak having the same mass in both the parent compound and the metabolite is extracted (S 4 ), and a complementary peak appearing at a position corresponding to the difference between the mass of the common peak and that of the precursor ion is extracted (S 5 ); the complementary peak corresponding to a common peak located on the product ion spectrum appears on the neutral loss spectrum, while the complementary peak corresponding to a common peak located on the neutral loss spectrum appears on the product ion spectrum. In the process of displaying the four spectrums in an integrated form, different display colors are assigned to the common peak, complementary peak and other peaks so that the different peaks can be easily distinguished (S 6  to S 9 ).

TECHNICAL FIELD

The present invention relates to a mass analysis data processing systemfor processing data obtained by a mass spectrometer capable of an MS^(n)analysis, where n is an integer greater than one.

BACKGROUND ART

In the field of mass analysis using an ion trap mass spectrometer orother apparatuses, a technique called the MS/MS analysis (or tandemanalysis) is conventionally known. In a general MS/MS analysis, an ionhaving a specific mass (or mass-to-charge ratio, m/z, to be exact) isfirst selected as a precursor ion from an object to be analyzed. Next,the selected precursor ion is dissociated by a collision induceddissociation (CID) process to produce product ions (also called fragmentions). The resulting product ions are subjected to a mass analysis toobtain information relating to the mass of the product ions, the ionsand neutral molecules desorbed by the dissociation operation, and otherparticles. Based on this information, the composition and chemicalstructure of the target sample molecule are deduced.

In recent years, samples to be analyzed with this type of system havebeen progressively increasing in molecular weight and becoming morecomplex in structure (or the composition). Therefore, depending on thenature of the sample, it is possible that the sample cannot bedissociated into sufficiently small masses by only one stage of thedissociation process. In such a case, an MS^(n) analysis may beperformed, where the dissociation operation is repeated two or moretimes and the eventually obtained product ions are subjected to massanalysis (for example, refer to Patent Document 1, 2 or otherdocuments). The aforementioned MS/MS analysis is an MS^(n) analysiswhere n=2.

In general, mass spectrometers create a mass spectrum (MS^(n) spectrum),with the horizontal axis indicating the mass-to-charge ratio and thevertical axis indicating the signal intensity (relative intensity), asthe result of mass analysis and presents it on a display screen as oneof the analysis results. In the case of a mass spectrometer capable ofMS^(n) analyses, a plurality of precursor ions having different massescan be respectively selected, in which case an MS^(n) spectrum will beobtained for each precursor ion. An MS^(n) spectrum provides varioustypes of peak information reflecting the state of the molecular bonds ofthe original compound. Accordingly, a plurality of compounds havingsimilar structures are likely to show MS^(n) spectrums having similarpatterns.

By the way, analyzing metabolites resulting from chemical changes in aliving organism is a crucial subject in many fields, such as thediagnosis of various kinds of diseases and illnesses, the assessment ofthe effectiveness and safety of drugs and functional foods, and theresearch on lifestyle and health. In recent years, a method calledMetabolomics for exhaustively analyzing a metabolite has been attractingattention. In this metabolite analysis, the aforementioned method usingMS^(n) spectrums is useful to search for a compound resulting from ametabolism of another compound having a known structure (this compoundwill be hereinafter called a “parent compound”, and the former compoundwill be called a “metabolite”). This is due to the fact that ametabolite results from a partial modification in the structure of aparent compound and their MS^(n) spectrums include many common features.Accordingly, by comparing their MS^(n) spectrums, it is possible toextract candidates for the metabolite from a large number of compounds.Software programs for automatically performing the analysis processdescribed to this point have been already provided.

However, to achieve the ultimate objective, i.e. the deduction anddetermination of the structure of a metabolite, an analysis operatorneeds to visually check MS^(n) analysis data and other data and make ajudgment. Improving the efficiency of this task has been a majorchallenge to enhance the throughput of the analysis. One reason for theinefficiency of this checking task is that it is difficult toimmediately, or intuitively, visually identify the peak that correspondsto the modified portion of the parent compound or metabolite in theMS^(n) spectrum. Another reason is that, even when it is appropriate toincrease the number of stages of the dissociation operation (i.e. toperform the MS^(n) analysis with a large value of n), it is not easy todecide which peak should be given priority to be the precursor ion forthe next stage.

Patent Document 1: Japanese Unexamined Patent Application PublicationNo. H10-142196

Patent Document 2: Japanese Unexamined Patent Application PublicationNo. 2001-249114

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

The present invention has been developed to solve the aforementionedproblems, and its objective is to provide a mass analysis dataprocessing system capable of providing useful information for performingan analysis of a plurality of components with similar chemicalstructures, e.g. the deduction of chemical structures, by using MS^(n)spectrums of the components in question.

Means for Solving the Problems

The present invention aimed at solving the previously described problemsis a mass analysis data processing system for processing mass analysisdata collected by using a mass spectrometer capable of an MS^(n)analysis (where n is an integer greater than one), the mass analysisdata being obtained by an MS^(n) analysis on an ion having a specificmass as a precursor ion for each of at least two components inclusive ofa first component and a second component, which is characterized byincluding:

a) an MS^(n) spectrum creating means for creating an MS^(n) spectrumbased on the mass analysis data obtained for each of the first componentand the second component;

b) an MS^(n) mass-difference spectrum creating means for calculating,for each of the two MS^(n) spectrums, a mass difference between the massof each peak among some or all of the peaks appearing on the MS^(n)spectrum and the mass of the precursor ion, and for creating an MS^(n)mass-difference spectrum having a peak at each calculated massdifference;

c) a common-peak extracting means for extracting a common peak havingthe same mass in the two MS^(n) spectrums relating to the firstcomponent and the second component and/or the two MS^(n) mass-differencespectrums relating to the first component and the second component;

d) a complementary-peak extracting means for extracting a complementarypeak on the MS^(n) spectrum and/or the MS^(n) mass-difference spectrumrelating to the first component and/or the second component, thecomplementary peak corresponding to a mass difference between the massof the precursor ion used in the MS^(n) analysis for the first componentand/or the second component and the mass of the common peak; and

e) a display control means for showing the MS^(n) spectrum and/or theMS^(n) mass-difference spectrum on a display screen, with thecomplementary peak having a style visually distinguishable from that ofthe other peaks on the MS^(n) spectrum and/or the MS^(n) mass-differencespectrum relating to the first component and/or the second component.

An example of the mass spectrometer capable of an MS^(n) analysis is anion-trap mass spectrometer using an ion trap, which is typically athree-dimensional quadrupole ion trap. The dissociation of precursorions is normally achieved by collision-induced dissociation. However,other methods may be used to dissociate precursor ions.

Any components may be chosen as the first component and the secondcomponent. However, applying the present invention to two componentshaving totally different chemical structures will produce no significantresults. Therefore, it is practically useful to choose two componentshaving similar chemical structures. For example, given a certaincompound as the first component, a metabolite produced from thiscompound by a metabolism in a living organism or other environments maybe chosen as the second component.

The “visually distinguishable” style is represented, for example, by adifferent color, thickness or type of the line of a peak, or anycombination of these properties. Instead of changing the lines of thepeaks, it is possible to change the color or other properties of themass labels numerically showing the mass information or other data ofthe peaks.

In the present invention, the MS^(n) spectrum is a mass spectrumreflecting the intensity of the product ions (or residual precursor ionsthat have not been dissociated) actually detected by a detector in themass spectrometer. By contrast, the MS^(n) mass-difference spectrumchanges its meaning depending on the valence of the precursor ion. Ifthe precursor ion is monovalent, the MS^(n) mass-difference spectrumreflects the intensity of neutral molecules that have been desorbed andexcluded from the precursor ion by dissociation (neutral loss);therefore, this spectrum can be regarded as a virtual mass spectrumrelating to some substances that have not been actually detected. If theprecursor ion is multivalent, the MS^(n) mass-difference spectrumreflects the intensity of the desorbed ions that have been actuallydetected.

For example, the complementary peak on the MS^(n) mass-differencespectrum relating to the first component is the peak that appears at amass value of Mb−Ma, where Ma is the mass of a common peak on the MS^(n)spectrums relating to the first and second components and Mb is the massof the precursor ion used in the MS^(n) analysis of the first component(Mb>Ma). On the other hand, the complementary peak on the MS^(n)spectrum relating to the first component is the peak that appears at amass value of Mb−Mc, where Mc is the mass of a common peak on the MS^(n)mass-difference spectrums relating to the first and second componentsand Mb is the mass of the precursor ion used in the MS^(n) analysis ofthe first component (Mb>Mc).

Similarly, the complementary peak on the MS^(n) mass-difference spectrumrelating to the second component is the peak that appears at a massvalue of Md−Ma, where Ma is the mass of a common peak on the MS^(n)spectrums relating to the first and second components and Md is the massof the precursor ion used in the MS^(n) analysis of the second component(Md>Ma). On the other hand, the complementary peak on the MS^(n)spectrum relating to the second component is the peak that appears at amass value of Md−Mc, where Mc is the mass of a common peak on the MS^(n)mass-difference spectrums relating to the first and second components Mcand Md is the mass of the precursor ion used in the MS^(n) analysis ofthe first component (Md>Mc).

The mass analysis data processing system creates at least four massspectrums, i.e. the MS^(n) spectrum relating to the first component, theMS^(n) mass-difference spectrum relating to the first component, theMS^(n) spectrum relating to the second component and the MS^(n)mass-difference spectrum relating to the second component. (Each of themis normally in the form of a graph with the horizontal axis indicatingthe mass and the vertical axis indicating the relative intensity.) It isnot always necessary to simultaneously display all of them.

However, it is preferable to simultaneously show all the mass spectrumson the same display screen so that one can at a glance compare the firstand second components and recognize the relationship between a commonpeak and a complementary peak corresponding to it. For that purpose, itis preferable to provide the display control means with the function ofdetermining the arrangement of the MS^(n) spectrum and the MS^(n)mass-difference spectrum relating to the first component as well as theMS^(n) spectrum and the MS^(n) mass-difference spectrum relating to thesecond component so that all the spectrums will be shown on the samedisplay screen.

For example, the MS^(n) spectrums of the first and second components maybe symmetrically arranged with respect to the mass axis. Similarly, theMS^(n) mass-difference spectrums of the first and second components canalso be symmetrically arranged with respect to the mass axis. In thiscase, the common peaks having the same mass extend in an approximatelyvertical direction, penetrating through the mass axis. Common peaksdrawn in this manner are easy to locate.

EFFECT OF THE INVENTION

When the first and second components have similar chemical structures,the common peak that appears on the MS^(n) spectrums or MS^(n)mass-difference spectrums of the two components reflects an ion orneutral molecule present at a portion (chemical structure) common to thefirst and second components. Conversely, the complementary peak reflectsa portion that is not common to the first and second components. Inother words, this peak reflects a portion characteristic of, or specificto, either the first or second component. Particularly, in the casewhere this characteristic portion is desorbed in the form of a neutralmolecule by the dissociation of a precursor ion, the peak correspondingto this neutral molecule cannot appear on normal MS^(n) spectrums butwill appear on the MS^(n) mass-difference spectrums created by the dataprocessing system according to the present invention. Furthermore, thispeak is shown in a special style and can be easily distinguished fromthe other peaks, so that the analysis operator can at a glance recognizethe portion concerned. This will improve the efficiency of the chemicalstructure analysis.

In the case where the mass corresponding to the complementary peakappearing on the MS^(n) spectrum is still large, it is preferable toproceed to the next n+1-th stage of dissociation operation and performan MS^(n+1) analysis using an ion corresponding to the complementarypeak as the precursor ion. In such a case, the task of settingparameters and commands necessary for the next analysis can beefficiently performed with the data processing system according to thepresent invention since the complementary peak can be instantaneouslylocated on the MS^(n) spectrum as well.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall configuration diagram of one embodiment of a massanalyzing system including a data processing system according to thepresent invention.

FIG. 2 is a flowchart showing the steps of a spectrum-displaying processperformed by the mass analyzing system of the present embodiment.

FIG. 3 is a diagram showing an example of two MS^(n) spectrums displayedby the mass analyzing system of the present embodiment.

FIG. 4 is a model diagram for explaining a method of displaying MS^(n)spectrums by the mass analyzing system of the present embodiment.

FIG. 5 is a chart for explaining the method of displaying MS^(n)spectrums by the mass analyzing system of the present embodiment.

FIG. 6 is a chart for explaining the method of displaying MS^(n)spectrums by the mass analyzing system of the present embodiment.

EXPLANATION OF NUMERALS

-   1 . . . Mass Analyzer Unit-   2 . . . Ion Source-   3 . . . Ion Optical System-   4 . . . Ion Trap-   5 . . . Time-of-Flight Mass Separator (TOF)-   6 . . . Detector-   10 . . . Central Controller-   11 . . . Analysis Controller-   12 . . . Data Processor-   13 . . . Operation Unit-   14 . . . Display Unit

BEST MODE FOR CARRYING OUT THE INVENTION

One embodiment of a mass analyzing system including a data processingsystem according to the present invention is hereinafter described withreference to the drawings. FIG. 1 is an overall configuration diagram ofthe present mass analyzing system.

A mass analyzer unit 1 includes an ion source 2 for ionizing samplemolecules, a three-dimensional quadrupole ion trap 4 for temporarilystoring ions within its internal space and for promotingcollision-induced dissociation of these ions, an ion optical system 3for guiding the ions produced by the ion source 2 to the ion trap 4, atime-of-flight mass separator (TOF) 5 for separating ions emitted fromthe ion trap 4 according to their mass (or mass-to-charge ratio, m/z, tobe exact) and a detector 6 for detecting the ions separated by the TOF5.

An analysis controller 11 conducts an MS^(n) analysis by controlling theoperation of each component of the mass analyzer unit 1 according to theinstructions from a central controller 10. A data processor 12 receivesdetection signals from the detector 6, converts them into digital dataand performs a predetermined data processing inclusive of a displayprocess which will be described later. An operation unit 13 and displayunit 14, which constitutes a user interface, are connected to thecentral controller 10. Most of the functions of the central controller10, analysis controller 11 and data processor 12 can be embodied by apersonal computer with appropriate controlling and processing softwareprograms installed therein.

The basic operation of the mass analyzing system having the previouslydescribed configuration is hereinafter schematically described. When anMS¹ analysis, i.e. a normal mass analysis with no dissociationoperation, is to be performed, the system operates as follows under thecontrol of the analysis controller 11: The ion source 2 ionizes samplemolecules to produce various kinds of ions. These ions are thenintroduced through the ion optical system 3 into the ion trap 4. Withinthe ion trap 4, the ions are temporarily captured by a quadrupoleelectric field formed by a radio-frequency voltage applied from a powersource (not shown) to the electrodes. Subsequently, at a specifictiming, kinetic energy is simultaneously given to all the ions capturedin the ion trap 4, whereby the ions are ejected from the ion trap 4 andintroduced into the TOF 5. This means that the ion trap 4 corresponds tothe start point where the ions begin their flight to the TOF 5. Whileflying through the flight space inside the TOF 5, the ions aretemporally separated according to their mass. The separated ionssequentially arrive at, and are detected by, the detector 6.

The data processor 12 receives this detection signal and converts thetime of flight within the TOF 5 to the mass to create a mass spectrumwith the horizontal axis indicating the mass and the vertical axisindicating the relative intensity. This mass spectrum is displayed viathe central controller 10 on the screen of the display unit 14. Based onthis mass-analysis result, the person in charge of the analysis (who ishereinafter called “the analyzer”) designates one ion as a precursor ionfor an MS² (MS/MS) analysis including one stage of the dissociationoperation.

When the analyzer enters, for example, the mass of the precursor ionthrough the operation unit 13 and gives a command to carry out the MS²analysis, the system operates as follows under the control of theanalysis controller 11: The ion source 2 ionizes sample molecules toproduce various kinds of ions. These ions are then introduced throughthe ion optical system 3 into the ion trap 4. Within the ion trap 4, theions are temporarily captured by the aforementioned quadrupole electricfield, immediately after which a voltage for dissipating unwanted ionsother than the previously selected precursor ion is applied to theelectrodes. As a result, only the precursor ion is left within the iontrap 4 (the selection of the precursor ion). Additionally, a CID gas isintroduced from an external source. The precursor ion is dissociated dueto the collision with the CID gas, whereby various kinds of product ionsare produced according to the mode of dissociation.

The product ions produced by the dissociation (and the residualprecursor ion, if it remains) are collectively ejected from the ion trap4 at a predetermined timing and introduced into the TOF 5. As in thecase of the normal mass analysis, the ions are temporally separatedaccording to their mass while flying within the flight space of the TOF5, and the separated ions sequentially arrive at, and are detected by,the detector 6. The data processor 12 receives this detection signal andconverts the flight time within the TOF 5 to the mass to create an MS²spectrum. This MS² spectrum is displayed via the central controller 10on the screen of the display unit 14.

It is also possible to perform an MS^(n) analysis with n=3 or a greaternumber by repeating the dissociation operation in stages, where one ofthe product ions produced within the ion trap 4 in one stage of thedissociation process is chosen as a new precursor ion to be dissociatedby the CID process. Although there is no theoretical limit on the numberof stages of the dissociation operation, the maximum value of n ispractically within the range from 3 to 6.

The data processor 12 in the mass analyzing system of the presentembodiment performs a characteristic operation when it creates a set ofinformation to be displayed on the display unit 14 after receiving thedetection signals obtained by the MS^(n) analysis. This operation ishereinafter described with reference to FIGS. 2 to 6.

As one example, the following description deals with the case of thestructural analysis of a metabolite (labeled “B”) originating from aparent compound (labeled “A”) having a known chemical structure. FIG. 2is a flowchart showing the steps of a spectrum-displaying processcharacteristic of the mass analyzing system of the present embodiment.

First, with the mass analyzing system shown in FIG. 1, an MS² analysisis respectively performed on both the parent compound (A) and metabolite(B) to collect MS² spectrum data for these compounds (Step S1). In thepresent example, the mass of the precursor ion used in the MS² analysisfor the parent compound (A) is 475, and that of the precursor ion in theMS² analysis for the metabolite (B) is 455. FIG. 3 shows examples of theMS² spectrum of the parent compound (A) and that of the metabolite (B).Although the peak corresponding to the precursor ion in each spectrumdoes not actually exist, the figure shows this peak by a dotted line foreasier understanding of the following description. The MS² spectrumsshown in FIG. 3 illustrate the intensity of the product ions and henceare hereinafter referred to as the “product ion spectrums.”

After the data have been collected in the previously described manner,when the data processing is initiated, the data processor 12 creates aproduct ion spectrum, as shown in FIG. 3, based on each set of thecollected data (Step S2). In this step, a peak list, which relates eachmass to an intensity, is created. This peak list can be graphicallyrepresented to obtain the product ion spectrum, in which the listedpeaks are drawn on a graph with the horizontal axis indicating the massand the vertical axis indicating the intensity.

Next, for the parent compound (A) and the metabolite (B), respectively,the mass difference between the mass of the precursor ion and the massof each product ion appearing on the product ion spectrum (i.e. listedin the aforementioned peak list) is sequentially calculated for eachproduct ion. Then, a mass-difference peak list, which relates each massdifference to the intensity of the product ion that has been the originof the mass difference, is created. For example, in the case of FIG. 3(a) where the mass of the precursor ion is 475, a product ion having amass of 150 has a mass difference of 325, and this mass difference isrelated to the intensity of the peak of the product ion having a mass of150 and registered in the mass-difference peak list. This operation issimilarly performed for each and every peak appearing on the product ionspectrum to complete a mass-difference peak list. A graphicalrepresentation of this peak list is the aforementioned MS²mass-difference spectrum, in which the listed peaks are drawn on a graphwith the horizontal axis indicating the mass and the vertical axisindicating the intensity. The mass difference corresponds to the mass ofa fragment desorbed from the precursor ion due to the dissociation. Onthe assumption that the precursor ion is monovalent, the desorbedfragment is a neutral molecule. Accordingly, the MS² mass-differencespectrum is hereinafter called the “neutral loss spectrum” (Step S3).

By the processes in Steps S2 and S3, the product ion spectrum andneutral loss spectrum relating to the parent compound (A) and thosespectrums relating to the metabolite (B) are created. Subsequently, thepeak list of the parent compound (A) and that of the metabolite (B) arecompared to locate a peak having the same mass and extract this peak asa common peak. The same process is also performed on the mass-differencepeak list of the parent compound (A) and that of the metabolite (B) toextract a common peak from both lists (Step S4).

Next, for each of one or more common peaks appearing on the product ionspectrum of the metabolite (B), the mass of a complementary peak to bepaired with the common peak in question is calculated. The phrase “to bepaired” means that the total of the masses of the common peak andcomplementary peak should equal the mass of the precursor ion. The massof the complementary peak to be paired with a given common peak can beobtained by subtracting the mass of the common peak from that of theprecursor ion. For example, the peak with a mass of 150 in FIG. 3( b) isa common peak and should have the complementary peak located at a massof 305 on the neutral loss spectrum since subtracting 150 from 455 (i.e.the mass of the precursor ion) comes to 305. The mass of a complementarypeak to be paired with each of one or more common peaks appearing on theneutral loss spectrum of the metabolite (B) can also be similarlycalculated. After the masses of the complementary peaks are thuscalculated, these complementary peaks are extracted from both the peaklist and the mass-difference peak list (Step S5).

Subsequently, a spectrum display integration process for showing thefour spectrums (product ion spectrums and neutral loss spectrums)created in Steps S2 and S3 on the same display screen is performed (StepS6). In the present embodiment, as shown in FIG. 4, the product ionspectrum P1 of the metabolite (B) and the product ion spectrum P4 of theparent compound (A) are symmetrically arranged with respect to thehorizontal mass axis, and the neutral loss spectrum P2 of the metabolite(B) and the neutral loss spectrum P4 of the parent compound (A) are alsosymmetrically arranged with respect to the same horizontal mass axis,with each neighboring pair of the product ion spectrum and neutral lossspectrum being symmetrically arranged with respect to the verticalintensity axis.

FIG. 5 is an example of the display format for integrating the production spectrums of the parent compound (A) and the metabolite (B) shown inFIG. 3 as well as the neutral spectrums derived from those product ionspectrums. In this example, each common peak is represented by a pair oflines that respectively extend upwards and downwards from the mass axis.In order to highlight the common peaks in both the product ion spectrumand neutral loss spectrum of the metabolite (B), the display color forthe common peaks are set so that they are drawn in a color differentfrom the color of the other peaks (Step S7). It should be noted thatthis difference in color cannot be actually represented in FIG. 5 andthe dotted lines are used in the figure to identify the common peaks tobe drawn in a different color. As shown, the product ion spectrums havethree common peaks at masses of 150, 190 and 250, while the neutral lossspectrums have two, at masses of 90 and 100.

Furthermore, in order to highlight the complementary peaks in both theproduct ion spectrum and neutral loss spectrum of the metabolite (B),the display color for the complementary peaks are also set so that theyare drawn in a color different from the color of the other peaks (StepS8). For example, the common peaks may be drawn in red, thecomplementary peaks in blue, and the other peaks in black. FIG. 6 is anexample in which the complementary peaks are also drawn in a differentstyle. It should be noted once more that this difference in style cannotbe actually represented in FIG. 6 and the complementary peaks to whichthe different display color should be applied are drawn in the chainedlines. The product ion spectrum has three complementary peaks at massesof 355 and 365, while the neutral loss spectrum has three, at 205, 265and 305. The arrowed lines, which show the relationships between thecommon peaks and the complementary peaks, may or may not be actuallydrawn on the display screen.

The mass spectrums that have been created in an integrated form in StepS6, using the display colors selected in Steps S7 and S8, as shown inFIG. 6, are displayed on the screen of the display unit 14 (Step S9). Byviewing this graphical presentation, the analysis operator can easilyrecognize the common peaks and obtain information relating to thestructure common to both the parent compound (A) and the metabolite (B).Additionally, the complementary peaks appearing in the metabolite (B)can also be easily recognized, so that the analyzer can intuitivelyobtain information relating to the portion characteristics of themetabolite (B), i.e. the site of metabolism. Thus, the task of deducingthe chemical structure of the metabolite (B) can be efficientlyperformed.

The ions corresponding to the complementary peaks appearing on theproduct ion spectrum of the metabolite (B) still have large masses.Their structure of these ions can be more clarified by furtherdissociating them into smaller product ions and analyzing the masses ofthese product ions. Accordingly, it is possible to select one of theions corresponding to the complementary peaks appearing on the production spectrum as the precursor ion for the next, MS³ analysis. Thisselection of the precursor ion can also be made by the present system.

Other than changing the display color of the peaks, there are manypossible methods for highlighting the common peaks and complementarypeaks. For example, the line type may be changed, as just shown in FIGS.5 and 6, or the line thickness may be changed. Instead of the line colorof the peaks, the color of the labels indicating the mass values may bechanged. Overlaying an additional marker is also possible. In theexample of FIGS. 5 and 6, although the display color of the common peakswas changed only in the product ion spectrum and the neutral lossspectrum of the metabolite (B), it is also possible to make a similarchange to the product ion spectrum and the neutral loss spectrum of theparent compound (A).

The form of integration of the four mass spectrums is not limited to theone shown in FIG. 4; for example, the four spectrums may be simplyaligned in a row. Displaying all the mass spectrums is not alwaysnecessary; for example, it is possible to display only the product ionspectrum and the neutral loss spectrum of the metabolite (B) in such amanner that the common peaks and the complementary peaks can bedefinitely distinguished from the other peaks.

In the previous embodiment, the display process was performed using theresult obtained by an MS^(n) analysis. It is naturally possible to applythe display process to a result obtained by an MS³ analysis, MS⁴analysis or other modes of MS^(n) analysis with n set to any valuesgreater than one.

In actual cases, one parent compound normally produces more than onekind of metabolites. Therefore, it is preferable to create a pluralityof display screens for individually comparing the product spectrum andneutral spectrum of the parent compound to those of the metabolites,with a browsing function for arbitrarily viewing the results relating tothe different metabolites by simple operations, such as selecting one ofthe tabs.

Furthermore, any changes, modifications or additions appropriately madewithin the spirit of the present invention in any other aspects of thesystem will naturally fall within the scope of claims of this patentapplication.

1. A mass analysis data processing system for processing mass analysisdata collected by using a mass spectrometer capable of an MS^(n)analysis (where n is an integer greater than one), the mass analysisdata being obtained by an MS^(n) analysis on an ion having a specificmass as a precursor ion for each of at least two components inclusive ofa first component and a second component, which is characterized bycomprising: a) an MS^(n) spectrum creating means for creating an MS^(n)spectrum based on mass analysis data obtained for each of the firstcomponent and the second component; b) an MS^(n) mass-differencespectrum creating means for calculating, for each of the two MS^(n)spectrums, a mass difference between a mass of each peak among some orall of peaks appearing on the MS^(n) spectrum and a mass of theprecursor ion, and for creating an MS^(n) mass-difference spectrumhaving a peak at each calculated mass difference; c) a common-peakextracting means for extracting a common peak having a same mass in thetwo MS^(n) spectrums relating to the first component and the secondcomponent and/or the two MS^(n) mass-difference spectrums relating tothe first component and the second component; d) a complementary-peakextracting means for extracting a complementary peak on the MS^(n)spectrum and/or the MS^(n) mass-difference spectrum relating to thefirst component and/or the second component, the complementary peakcorresponding to a mass difference between the mass of the precursor ionused in the MS^(n) analysis for the first component and/or the secondcomponent and the mass of the common peak; and e) a display controlmeans for showing the MS^(n) spectrum and/or the MS^(n) mass-differencespectrum on a display screen, with the complementary peak having a stylevisually distinguishable from that of other peaks on the MS^(n) spectrumand/or the MS^(n) mass-difference spectrum relating to the firstcomponent and/or the second component.
 2. The mass analysis dataprocessing system according to claim 1, which is characterized in thatthe visually distinguishable style is represented by a different color,thickness or type of a line of the peak.
 3. The mass analysis dataprocessing system according to claim 1, which is characterized in thatthe display control means is provided with a function of determining anarrangement of the MS^(n) spectrum and the MS^(n) mass-differencespectrum relating to the first component as well as the MS^(n) spectrumand the MS^(n) mass-difference spectrum relating to the second componentso that all the spectrums will be shown on the same display screen. 4.The mass analysis data processing system according to claim 2, which ischaracterized in that the display control means is provided with afunction of determining an arrangement of the MS^(n) spectrum and theMS^(n) mass-difference spectrum relating to the first component as wellas the MS^(n) spectrum and the MS^(n) mass-difference spectrum relatingto the second component so that all the spectrums will be shown on thesame display screen.
 5. The mass analysis data processing systemaccording to claim 3, which is characterized in that the MS^(n)spectrums of the first and second components are symmetrically arrangedwith respect to the mass axis, and the MS^(n) mass-difference spectrumsof the first and second components are also symmetrically arranged withrespect to the mass axis.
 6. The mass analysis data processing systemaccording to claim 4, which is characterized in that the MS^(n)spectrums of the first and second components are symmetrically arrangedwith respect to the mass axis, and the MS^(n) mass-difference spectrumsof the first and second components are also symmetrically arranged withrespect to the mass axis.